Converting device



June 12, 1945. s MYERS 2,377,898

CONVERTING DEVICE Filed Dec. 12, 1941 235. REGISTERS.

Patented June 12, 1945 UNITED STATES' PATENT OFFICE CONVERTING DEVICE York Application December 12, 1941, Serial No. 422,709

2 Claims.

This invention relates to a device by which the displacement of an input member is converted into a rate of change of displacement of an output member which is proportional to a function of the input member displacement. The converting device is particularly adaptable for use in introducing a reciprocal function of time of flight as a rate of motion into fire control prediction instruments and in the control of computing mechanisms utilizing variable speed drives of the ball, drum and disc type.

A device of this character constructed in accordance with the present invention includes the combination of two rotatably mounted discs whose axes are arranged in parallel and eccentric relation, one of the discs being rotated by suitable means at a substantially constant speed and the other of the discs forming an output member which is variably driven by the constant speed disc. A rotatable member connects the two discs and a displaceable input member positions the rotatable member along a line intersecting the axes of the discs to control the movement transmitted from the driver disc to the driven or output disc.

Other features and structural details of the invention will be apparent from the following description when read in connection with the accompanying drawing, wherein Fig. l is a schematic perspective view, in which the device constructed in accordance with the present invention is shown as applied to use with the ball, disc and drum mechanism of a fire contro1 prediction instrument, and

Fig. 2 is a detail schematic perspective view of a device embodying the present inventive concepts.

With reference to the drawing, the improved device by which the input member displacement is converted into a rate of change of displacement of the output member which is proportional to a function of the input member displacement includes in the combination of provided elements a disc or rotating member II] which is rotated at a substantially constant speed by means of a constant speed motor I I. The constant speed rotating disc I transmits its movement to a second disc or rotating member l2, which forms the output member of'the device, through intermediate means including a ball carriage supporting a pair of freely rotatable balls as indicated at M, the rotatable balls thereof simultaneously engaging both discs I!) and I2 and imparting movement to the output member from the disc driven by the constant speed motor I I. The axes of rotation of the respectve discs, as defined by shaft l5 for disc I0 and shaft l6 for disc l2, are arranged in parallel relationship. 7 Also, the mounting for the output member positions shaft IS in eccentric relation to the axis of the constant speed disc [0. The input member for the device is designated at l I, the same being linearly displaceable and being adapted to connect with or being integral with a portion of the ball carriage indicated at M. Member M, which transmits the motion of disc H! to output member or disc I2, is therefore controllably positioned by the input member I! along a, line intersecting the axes of the respective discs. Input member I! and the ball construction l4 may be considered as a single displaceable piece which operates within the range defined by the straight line distance between the axes of the eccentrically arranged dies and which further imparts the rotary movement of the constant speed disc to the output member. By the defined arrangement of parts, the linear displacement introduced in the device by the input member is converted into a rate of change of displacement of the output member which is proportional to a non-linear function of the input member displacement. Such a converting device is particularly useful in connection with the ball, drum and disc type of computing mechanism employed in fire control instruments, in which a three-dimensional time of flight cam is provided having a contour adapted to position a follower in accordance with a function of time of flight of the shell. Such a cam in a fire control director may be positioned in one dimension (e. g., rotated) in accordance with target altitude and positioned in another dimension (translated) in accordance with target horizontal or slant range, as shown, for example in U. S. Patent 2,206,875, dated July 6, 1940. In certain prior forms of prediction computing mechanisms, as ilustrated in the above patent, the lift of the cam follower, has been made directly proportional to the reciprocal of time of flight and this lift converted by a variable speed drive into a rate of rotation also directly proportional to In these earlier arrangements the contour of the cam is such that equal increments of a variable, e. g., range, produce unequal changes of the input of to the prediction computing mechanism and also the slope of the cam becomes very steep in certain regions, resulting in an abnormally high frictional load on the follower. As a result of the above-mentioned disadvantages the values of range which could be used to displace a cam in prior computing arrangements was greatly restricted. By the converting device of the present invention, comprising a pair of eccentrically rotatable discs, the lift of the cam follower necessary to produce an output rate of rotation proportional to becomes more nearly proportional to time of flight itself and the cam may be substantially conical in form. Such a contour is much easier to produce and avoids the regions of steep slope characteristic of prior art cams.

In the form of the invention shown in Fig. 1, the means for displacing the input member H is provided by a substantially conically shaped time of flight cam 20. The straight sloping side of the axially movable cam 20 engages the end of the input member I! and displaces the: same in accordance with a function of the predicted time of flight of a shell to a particular target position. The value introduced into the converting device by the input member positions the rotatable member l4 so that the output member I2 is driven by the disc ID to revolve at a rate which is proportional to a reciprocal function of the value of the rectilinear displacement of the input member minus an arbitrary constant and the cam is so designed that this rate of rotation of disc |2 becomes proportional to This relation may be shown mathematically by letting- M=the R. P. M. of the constant speed driving disc l0.

N=the instantaneous R. P. M. of the driven or output member I2.

D=the distance between shafts l6 and I5, and

r1=the instantaneous distance between the ball member construction l4 and the shaft Id of the output disc l2 which is representative of a given value of the displacement of the input member By the structural relation of the parts, then, for a given position M (D-n) =Nr1 Solving this equation for the instantaneous value of N, the R. P. M. of the output member l2, the result may be expressed as follows:

where M and D are constants.

When the rate of rotation of the output member is to be a measure of the reciprocal of time of flight, as in prediction computing mechanisms,

this last equation may be expressed as 1 M D T T] M where is measured as a rate of rotation. Solving the above equation for n in terms of T, we obtain the following particular function of time of flight which must be derived as the lift of cam 20 in order to produce an output speed of disc l2 proportional to MDT 1+MT It has been found that a cam designed to produce this function as the lift of its follower is substantially cone-shaped, a fact which allows the use of a much smaller cam for the same degree of accuracy as was obtained in prior art devices, wherein the cam had to be designed to produce the reciprocal function of time of flight.

The motion of rotatably mounted disc or output member |2 serves to introduce the factor into the prediction computing mechanism by way of shaft I6. As seen in Fig. 1, shaft I6 drives the disc of a second variable speed drive comprising driving disc 2|, ball assembly 22 and driven cylinder or drum 23. This second variable speed drive is interconnected to a mechanical differential 24 which receives an input by way of shaft 25 whose rate of rotation introduces another factor, in this case rate of target movement, into the prediction computing mechanism. Means for securing a measure of rate of target movement are described in aforementioned Patent 2,206,875. Shaft 25 is geared to one arm of the mechanical differential 24 by means of pinions 26 and 21. A second arm of the differential is controlled by the drum 23 by way of gears 28 and 29 through shaft 30. The third arm of the differential 24 positions a shaft 3| which through bevel gears 32 and 33, pinion 34 and rack 35 controls the longitudinal movement of ball carriage 22. It will be apparent that differential 24 acts as a speed equalizer to provide an automatic speed balance between shafts 25, 30. This equalizing action is exerted by the third arm of the differential which moves ball carriage 22 by way of intermediate driving members above described to a position causing cylinder 23 and shaft 30 to be driven from disc 2| at the same speed as shaft 25. In this position it wil be apparent that the speed of cylinder 23 and shaft 30 is proportional to the product of the speed of disc 2| and the radial displacement of ball carriage 22. By equating the speeds of cylinder 23 and shaft 25, it will be further seen that the radial displacement of ball carriage is proportional to the quotient of the speed of shaft 25 and the speed of disc 2|. By driving disc 2| at a speed proportional to the reciprocal of time of flight and shaft 25 at a rate proportional to the rate of change of target position, the radial displacement of ball carriage 22 is caused to be proportional to the quotient of these two quantities, or the product of rate of target displacement and time of flight, which is the prediction correction sought. By starting, then, with the condition that disc 2| is to be driven in proportion to it will be found from the equations presented L63" nemonuw. 6 1 5 hereinbefore that the slope of three-dimensional cam 20 may be made substantially constant in the axial direction, constituting a decided improvement over the arrangements of prior art which required a cam having, in many cases, an impractical contour because of the type variable speed converter which it controlled.

In prior predicting apparatus, therefore, the required rate of motion, proportional to the reciprocal of time of flight, was obtained by first obtaining a displacement proportional to the reciprocal of time of flight from the lift of a suitably designed cam, and then converting this displacement to a corresponding rate of motion, also proportional to the reciprocal of time of flight, by a conventional variable speed device. By employing the converting device of the present invention instead of the conventional variable speed device of prior systems, it is no longer necessary to design the cam to produce a lift proportional to the reciprocal of time of flight, which design is inconvenient and impractical, but it is only necessary to design the cam to have a lift equal to the particular function of time of flight, which, when employed to actuate the converting device of the present invention, will produce an output rate of motion proportional to the reciprocal of time of flight. A cam designed to have such a lift, since it can be substantially conical in shape, is much easier to lay out and can have a, greater accuracy over a larger range.

In the form of the invention shown in Fig. 2, a pointer and dial arrangement such as designated at 39 and 40, controlled from the input member ll and a crank arm piece 4| which drives the member I1 through the pinion 42 and rack 43 may be employed to introduce the desired function into the converting device. By making the scale 40 sufficiently non-linear to take account of the arbitrary constant M of the equations, an output speed of rotation of shaft l6 can be obtained which is proportional to the reciprocal of the value introduced by handwheel 4| as designated on scale 40.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is @UQKE Kati HUWBW intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A mechanism for a fire control device adapted to produce output data similar to that derived from a three dimension cam but capable of providing a greater range of data where the nature of that required is such as to necessitate a mechanically awkward cam shape for certain portions of the data, said mechanism comprising an approximately conical three dimension cam, a lift pin operated thereby, a ball carriage coupled to the lift pin, a pair of discs coupled by the ball carriage, the discs having parallel off-set shafts radially spaced a predetermined distance, the shaft of one disc being an output shaft, a constant speed drive coupled to the other shaft, the cam being so laid out as to actuate the lift pin in proportion to that particular function of the required data which is necessary to actuate the output shaft at a rate proportional to the reciprocal of the required output data.

2. A mechanism for a fire control device adapted to produce output data equivalent to that derived from the output of a three dimension cam but providing a greater range of data where the nature of the required cam output data is such as to necessitate a mechanically awkward cam shape for certain portions thereof, said mechanism as used with a time of flight computer comprising an approximately conical three dimension cam, a lift pin operated thereby, a ball carriage actuated by the lift pin, a pair of discs coupled by the ball carriage having parallel offset axes disposed with predetermined radial spacing, an output shaft connected to a first of the discs, a constant speed drive for the second disc, the cam being so laid out as to actuate the lift pin in proportion to that particular function of time of flight which is necessary to actuate the output shaft at a rate proportional to the reciprocal of the time of flight.

J EN'NIE B. MYERS, Executria: of the Estate of Shierfield G. Myers,

Deceased. 

